Eastern Coatings Show - 2017 Allen Bulick*, Chris LeFever, Glenn - - PowerPoint PPT Presentation

Film Properties and Formulation Considerations for Corrosion Resistance in Styrenated Acrylic Metal Coatings

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Eastern Coatings Show - 2017

Allen Bulick*, Chris LeFever, Glenn Frazee, Kailong Jin, Matt Mellott

*Technical Manager – Industrial & Construction allen.bulick@eps-materials.com, 815-568-4156

• Project Background
• Adhesion & Corrosion Protection Mechanisms
• Literature Review
• Commercial Resin Film Property Study
• Next Generation Development
• Formulation Considerations
• Conclusions

Agenda

Project Mandate Deliver best in class balanced, low VOC DTM resins Lower VOC demands result in higher technical complexity in an effort to maintain full balance of properties Interplay between adhesion and corrosion prompted in depth structure/property investigation

Project Background

Lower Tg (or low VOC plasticizer) to lower VOC reduces hardness and block resistance Some formulation mitigations available, but not ideal

– Fluorosurfactants

Performance Tradeoffs

Adhesion vs. Corrosion Resistance

~50μm DFT, 12PVC High Gloss, 400hr B117

Incumbent Prototype A Prototype B Prototype C Prototype D

Attempts at improving Al adhesion

Reduction of adhesion monomers

Adhesion/Corrosion Balance

B117, ~50μm DFT, CRS

CRS Wet CRS Dry CRS Wet CRS Dry CRS Dry

Prototype E 500 hrs 500 hrs Prototype F 500 hrs Prototype G

Adhesion to Steel

Fe Fe Fe Fe Fe Fe Fe C C C OH2

+

OH OH OH O- + + +

Lewis Base Sites Lewis Acid Sites

• Provided sufficient wetting is present, acid/base interactions, ionic interactions and van der Waals

forces considered of primary importance1

• Isoelectric point of steel difficult to pinpoint, but likely around pH ~8-9
• As ammonia evaporates and pH drops, cationic sites arise allowing for electrostatic interactions
• Mechanical interlocking also significant in blasted substrates

1Fowkes, F.M., J Polym Sci J Polym Chem Ed, 1984, 22, 547

Corrosion Process - Steel

Water O2 Anode Cathode Cathode e- e- Fe Fe2++ 2e- Fe2++ 2H2O Fe(OH)2 + 2H+ O2 + 2H2O + 4e- 4OH- O2 + 4H+ + 4e- 2H2O 4Fe(OH)2 + O2 Fe2O3•xH2O Fe2+ + 2OH- Fe(OH)2 Red Rust

Requires

– Water – O2 (CO2, or other reducible species) – Electrolytic pathway

Possible mechanisms of corrosion prevention

• Block water penetration
• O2 transport inhibition
• Adhesion – surface passivation, exclusion of water, etc
• Interference with electrolytic pathway – coating resistance

Barrier Properties

Literature Review

• S. Guruviah, JOCCA, 53, 1970, 660; P. Kresse, Pigment Resin

Tech, 2(11), 1973, 21

– O2 transport limiting factor in corrosion protection

Barrier Properties

• J. Mayne, Corrosion, 1976, pp15:24-15:37; Bacon, et al, Ind Eng

Chem, 40(1), 1948, 161

– Films generally too permeable for barrier properties to be important – Inhibition of galvanic cell via a high film resistance which impedes electrolyte transport most important factor

Impedance Adhesion

• W. Funke, H. Haagen, Ind Eng Chem Prod Res Dev, 17, 1978, 50;
• E. Parker, H. Gerhart, Ind Eng Chem, 59(8), 1967, 53

– Loss of adhesion leads to onset of corrosion

See appendix for further reading suggestions

Electrolytic Resistance

• Study of 300 coatings showed resistance thresholds of ~108Ohm

for the best coatings and at least ~106 Ohm for fair performance

Ind Eng Chem, 40(1), 1948, 161-167

• Coating resistance falls with increasing electrolyte concentration

Maitland CC, Mayne JEO, Official Digest, Sept 1962

• Inverse study between ion exchange capacity and corrosion

resistance of film

Ulfvarson, U and Khullar, M, JOCCA, 54, 604, 1971 Acrylic film as ion exchange system

Study Description

• 21 internal and external styrenated acrylic systems
• Wide variety of performance capabilities, Tg’s,

MFFTs, etc

• Formulated into single clear formulation – adjusted

coalescent level for MFFT

• Evaluated in a number of performance tests to

develop a film property/corrosion model

Study Design

Test*

B117 Corrosion** Cyclic Prohesion QUV Humidity Resistance Dry Adhesion Wet Adhesion Electrochemical Impedance Film Hardness Water Vapor Transmission Oxygen Transmission Liquid Water Uptake

Performance Properties Film Properties

*Tests in bold will be discussed here, other pieces will be tied into future presentations ** Panels were force ranked on a 1-10 scale for corrosion resistance, 10 being best

Corrosion Resistance

B117, CRS (4”6” R-series Q-panel), ~75μm DFT, 66hrs

Resin 1 Resin 2 Resin 3 Resin 4 Resin 5 Resin 6 Resin 7 Resin 8 Resin 9 Resin 10 Resin 11 Resin 12 Resin 13 Resin 14 Resin 15 Resin 16 Resin 17 Resin 18 Resin 19 Resin 20 Resin 21

Resin 1 Resin 2 Resin 3 Resin 4 Resin 5 Resin 6 Resin 7 Resin 8 Resin 9 Resin 10 Resin 11 Resin 12 Resin 13 Resin 14 Resin 15 Resin 16 Resin 17 Resin 18 Resin 19 Resin 20 Resin 21

Corrosion Resistance

B117, CRS (4”6” R-series Q-panel), ~75μm DFT, 230hrs

1 2 1 2 3 3 4 5 5 6 6 6 7 7 8 7 8 8 8 9 10

Resin 1 Resin 2 Resin 3 Resin 4 Resin 5 Resin 6 Resin 7 Resin 8 Resin 9 Resin 10 Resin 11 Resin 12 Resin 13 Resin 14 Resin 15 Resin 16 Resin 17 Resin 18 Resin 19 Resin 20 Resin 21

Corrosion Resistance

B117, CRS (4”6” R-series Q-panel), ~75μm DFT, 560hrs

Resin Pull-off Adhesion Corrosion rating Standard Dolly Resin 1 5 272.0 8 Resin 2 68.0 1 Resin 3 5 241.3 3 Resin 4 5 231.3 8 Resin 5 5 271.0 7 Resin 6 91.5 6 Resin 7 5 188.0 1 Resin 8 3 168.0 6 Resin 9 5 290.5 2 Resin 10 4 224.0 4 Resin 11 4 212.3 2 Resin 12 4 179.7 6 Resin 13 106.5 5 Resin 14 1 116.0 3 Resin 15 4 200.0 10 Resin 16 4 211.0 7 Resin 17 4 205.0 5 Resin 18 4 177.0 9 Resin 19 4 172.0 8 Resin 20 4 208.3 7 Resin 21 4 213.3 8

Dry Adhesion

10mil wet drawdown, CRS (4”6” R-series Q-panel)

Resins 30 min* 1 hr** 24 hr** 48 hr** 4 day** 1 wk** 2 wk** Average***

Resin 1

5 5 5 5 5 3 4.7

Resin 2

2 0.3

Resin 3

3 4 4 3 3 2 3.2

Resin 4

4 5 5 3 2.8

Resin 5

5 5 5 1 2.7

Resin 6

2 1 0.5

Resin 7

5 5 1.7

Resin 8

3 3 4 1.7

Resin 9

5 5 1.7

Resin 10

5 4 5 5 5 4.0

Resin 11

5 4 1.5

Resin 12

4 4 3 1.8

Resin 13

1 0.2

Resin 14

1 1 0.3

Resin 15

3 4 5 2.0

Resin 16

5 4 1.5

Resin 17

4 4 5 3 2 3.0

Resin 18

4 4 4 3 2 2.8

Resin 19

4 4 3 1.8

Resin 20

5 4 5 2.3

Resin 21

5 4 3 2.0 *adhesion after covering with wet paper towel; **adhesion after immersion in water; ***average through 1 week

Wet Adhesion

10mil wet drawdown, CRS (3”6” R-series Q-panel)

Adhesion/Corrosion Correlation

Corrosion Correlations

Impedance Studies

R2=0.61 p value = 8.85E-05

Next Generation Development

B117, ~50μm DFT, CRS

< 50g/L DTM Prototype

• Self-crosslinking styrenated acrylic
• Market leading corrosion resistance
• Excellent humidity resistance
• Good block resistance

Broad spectrum adhesion properties 700hrs New Prototype 350hrs Market Leading 50g/L DTM

Thin Film Corrosion Resistance

B117, CRS, 300hrs

Prototype shows competitive corrosion resistance to solvent based alkyd

50g/L Prototype 1mil DFT

Solventborne Alkyd Short Oil Chain Stopped

1mil DFT

Impact of P:B or PVC

48hr 285 hr

Corrosion resistance decreases with increasing P/B ratio (reproduced with

• ther resins)

Possible explanations:

• 1. Increased porosity with increasing P/B ratio; liquid water uptake increases
• 2. Interfacial layer around the pigment particles facilitates water migration and

increases diffusion

P/B = 0 P/B = 2 P/B = 0 P/B = 2

PVC On Liquid Water Uptake

Wet cup method NMR method

• Increasing PVC increases water uptake1
• Decreasing particle size increases water

uptake1

– Related to surface area

• Dispersant/pigment interface identified

as coating weak point1

• Liquid water uptake can also be

measured by EIS – related to corrosion resistance

• Acrylic coatings can take months to

achieve final barrier properties1

1Donkers, PA et al, Proc. of Europ. Coat. Conf.

Waterborne Coat., 2013

Resin in Grind

B117, ~50μm DFT, 300hrs, CRS Standard Resin in Grind

Importance of Formulation

B117, 1mil DFT, CRS, 500hrs

Surfactant Change

• Resin
• Coalescent
• Wetting agent
• Flash rust inhibitor
• Silicone defoamer
• HEUR thickener

Clear Formulation

Importance of Formulation

B117, 1mil DFT, CRS, 500hrs

Coalescent Change

• Resin
• Coalescent
• Wetting agent
• Flash rust inhibitor
• Silicone defoamer
• HEUR thickener

Clear Formulation

Conclusions

• Protective action of coatings on steel is a complex process with disagreement in

literature over relative importance of barrier properties, adhesion, and electrochemical impedance

• Experimental observations and more recent studies point towards impedance as

primary indicator of corrosion protection in B117 salt fog

• Other film properties may play a role in under different corrosion testing

conditions – e.g. cyclic prohesion, exterior exposure

• Study of 21 styrenated acrylics showed no correlation between adhesion

properties and corrosion resistance

• Adhesion still an important property in real world substrate protection

– Easily chipped/damaged coatings will leave parts of substrate unprotected

• Future work expands study to include barrier properties and impedance as well as
• ther accelerated testing methods – prohesion, QUV, humidity
• Learnings led to development of 50g/L DTM with previously unachieved balance of

adhesion and corrosion resistance

Acknowledgements

• Howard Killilea
• MJ Hibben
• Matt Andersson
• Zac Cowser
• Niteen Jadhav
• Dave Nevison

Questions?

Further Reading

• R.A. Dickie, F.L. Floyd, “Polymeric Materials for Corrosion Control,” ACS Symposium, 1986
• D. Greenfield, D. Scantlebury, “The Protective Action of Organic Coatings on Steel: A Review,”

JCSE, 3(5), 2000

• E. van Westing, “Determination of coating performance with impedance measurements,”

TNO Centre for Ctgs Res, 1992

• M. A. Butt, et al, “Theory of Adhesion and its Practical Implications,” J Faculty of Eng & Tech,

2007-2008, 21-45

• G. Bierwagen, et al, Prog in Org Ctgs, 46(2), 2003, 149
• F. Floyd, et al, Prog in Org Ctgs, 66(1), 2009, 8
• M. O’Donoghue, et al, Coatings & Linings, 2003, 36
• S. Shreeptahi, et al, J Coat Tech & Res, 8(2), 2011, 191
• C. Moreno, et al, Int J. Electrochem Sci, 7, 2012, 8444